The overall objective of this project is a better understanding of the mechanisms and factors which regulate proliferation. A model system has been developed in which quiescent human fibroblasts can be stimulated to replicate DNA and to divide by physiological concentrations of mouse epidermal growth factor (mEGF). This effect of mEGF is observed in the absence of added serum provided micromole concentrations of ascorbic acid are present and is further enhanced by the addition of an mEGF-binding arginine esterase isolated from the mouse submaxillary gland. The mechanism of mEGF action in this system as well as the roles of ascorbate and the esterase to modulate the growth response to the factor are under investigation. We are also studying the regulation of polyamine metabolism and the functions of these organic cations in growth. A rapid and marked induction of ornithine decarboxylase has been observed during growth stimulation elicited in cultured fibroblasts by serum shift-up. The mechanism of this effect is being studied as an approach to an understanding of early events during the onset of cell proliferation. Ornithine decarboxylase has been purified from mouse fibroblasts so as to prepare specific antiserum for detailed studies of the induction mechanism in both normal and transformed cells.